How Can One Tell What Telescope Made an Image of a Deep Space Object?

Question: When looking at an image of a deep space object,  how can you tell what type of telescope was used to take the photo?  — Jeni

Answer: Unless the caption or other description of the image lists the telescope used to make the image, it is often hard to tell which telescope was used to make an image of an astronomical object.  Fortunately, at least in my experience, the origin of an astronomical image is almost always listed with the information associated with the image.

Jeff Mangum

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Why are Telescopes Better at Observing Astronomical Objects than the Naked Eye?

Question: Why are telescopes better than the naked eye?  — Amanda

Answer: Well, in fact, there are circumstances when the naked eye is a better way to observe astronomical phenomena than a telescope.  For example, if you are interested in viewing the general structure of the night sky, such as constellations or the dust lanes what comprise the Milky Way, you are better off using just your eyes, as a telescope would restrict you to observing just a small region of the sky.  Telescopes, on the other hand, are best for getting a very close-up look at the details of most astronomical objects, including planets, stars, and galaxies.  Telescopes allow you to see details, due to their higher spatial resolution, than one can see with the naked eye.

Jeff Mangum

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What if the Big Bang Started as a Gigantic Supernova and Associated Black Hole?

Question: A cosmological “what if ”
Here’s my question:

suppose for the sake of argument, the big bang happened somewhat differently, that it was like a huge mega supernova, and created super-duper massive black hole. A universal black hole. THE black hole of the entire known universe!

slowing down all the stuff that blew away from it.
the stuff coalesced into galaxies which are all still expanding away from each other.

such a scenario would have all the galaxies at different heights in a huge potential well. now…if our galaxy were further up such a potential well, all the light from all the galaxies further down would be red shifted.

also photons emitted from those galaxies would not only come ‘straight’ up the potential well but also would spiral up the potential well.

If our galaxy were near the ‘top’, light from one galaxy would reach us from many directions, all such photons would be red-shifted, and would have taken different lengths of time to reach us because of the many different spiral geodisics they could have taken. In other words, many of the galaxies we see could in fact be the SAME galaxy seen from a different direction in the sky and at vastly different times in its evolution as well as from its different orientations.

pretty much all the galaxies would appear to be receeding from ours (whether they are or not)

furthermore, between our galaxy and the more red-shifted ones further down the well,  the space-time would become more and more stretched the further away from our galaxy you’d go.
And therefore it would appear that the expansion of the universe was therefore ‘speeding up’.

Thus explaining the embarassing ‘dark’ energy issue.

In other words, all the distant galaxies might not be ‘spread out’ over the night sky as they appear to be, but instead be all more or less in the same ‘direction’ (downwards), in one and the same huge potential well of “THE” black hole of the entire Universe, that would make a galactic supermassive black hole look like an electron neutrino!

There would be no ‘center’ because any such center would be in all directions, it would therefore be ‘spread out’ as the surface of a sphere.

So maybe therefore, our view of the universe has been ‘inside out’ as it were.

This view seems consistent with general relativity.

How would we know? observationally, how could we tell the difference?
(it sure would explain the ‘dark’ energy /cosmic acceleration issue, plus it’s a lot less absurd)

— Tom


Answer: I think that your scenario has one basic flaw in that if the giant supernova which led to the “central” black hole did exist, we would observe a “source” or center for the overall expansion of the universe.  In fact, what we see are all galaxies (excluding local gravitational interactions between galaxies located near each other) moving away from each other rather than moving away from a common point.  You might want to take a look at some of the questions and answers that have been posted to the cosmology section of this blog for further information.


Jeff Mangum

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Availability of VLA Measurements of M87?

Question: I am contacting you on behalf of the MAGIC collaboration. I was wondering whether you took with VLA any further data on M87. We are trying to get an MWL coverage for our observation period spanning from 2012 to 2015. What we would need is the lightcurve for these years and a skymap. — Cornelia

Answer: In fact, you can search the VLA data archive, which contains all of the data acquired by the VLA since it started observations in 1976, for observations of M87.  Go to to access the NRAO science data archive (which contains the VLA science data).  You will need to generate the images from these measurements yourself, and also any lightcurve derived from these measurements.

Jeff Mangum

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Which Planet Orbits our Sun the Fastest?

Question: Which planet in our solar system is orbiting the sun at the fastest speed?  — Mike

Answer: Mercury is the winner at an orbital speed of about 47.87 km/s (107,082 miles per hour), which is a period of about 87.97 Earth days.  Just for your information, here is a list of the orbital speeds (and periods) for all 8 (plus Pluto) planets:

  • Mercury: 47.87 km/s (107,082 miles per hour), or a period of about 87.97 days
  • Venus: 35.02 km/s (78,337 miles per hour), or a period of about 224.7 days
  • Earth: 29.78 km/s (66,615 miles per hour), or a period of about 365.256365 days
  • Mars: 24.077 km/s (53,853 miles per hour), or a period of about 686.93 days
  • Jupiter: 13.07 km/s (29,236 miles per hour), or a period of about 11.86 years
  • Saturn: 9.69 km/s (21,675 miles per hour), or a period of about 29.42 years
  • Uranus: 6.81 km/s (15,233 miles per hour), or a period of about 83.75 years
  • Neptune: 5.43 km/s (12,146 miles per hour), or a period of about 163.72 years
  • Pluto: 4.74 km/s (10,603 miles per hour), or a period of about 247.92 years

Jeff Mangum

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Does the Coriolis Effect From the Milky Way Rotation Influence the Orbits of Planets in our Solar System?

Question: I read that our solar system orbits the center of the Milky Way Galaxy and am wondering if orbital direction of the planets was initially influenced by the Coriolis effect.  — Jack

Answer: Two comments to your question.  First, the net orbital angular momentum axis of the Sun or the Solar System turns out not to be aligned with the “spin axis” of our Milky Way galaxy.  The plane of the disk of our Solar System is inclined by an angle of about 63 degrees relative to the plane of the Milky Way within which our Solar System resides.  Second, the Coriolis effect, sometimes referred to as a “fictitious force”, refers to motion which is really in a straight line, but which appears to be curved when viewed from a reference frame that is accelerating (i.e. rotating).  So, if you are in a rotating disk, like our Solar System, you experience a Coriolis force, but if you step away from our Solar System and look at it from a point that is not accelerating, you would see planets in motion but with no Coriolis effect.

Jeff Mangum

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What is a Black Hole Made of?

Question: I googled this question while looking for an answer to something even more vague:  what is a black hole made of?   If the 3 observable properties or a black hole are supposed to be mass, charge, and angular momentum, then what “inside” the black hole can still provide those properties if all matter in a black hole has supposedly been destroyed?   The only thing I’ve been able to imagine is that a black hole does not actually destroy any matter that falls into it … it just prevents us from observing it.    Otherwise the implication is that mass, charge, and angular momentum can exist independently of matter.  — Rob

Answer: As you already know, black holes are places where extreme gravitational attraction draws everything, even light, to a single point in space.  The problem with understanding exactly what happens to the stuff that pulled into a black hole is that physicists really don’t have a complete understanding of how gravity works under the extreme conditions found in a black hole.  Called “quantum gravity”, an understanding of how gravity works in a black hole requires physicists to figure out what happens to gravity at atomic-scale levels.  The physical properties of a black hole, which as you have said are mass, charge, and angular momentum, are measurable and are properties that derive from the event horizon of the black hole.  Inside the event horizon, which is where quantum gravity effects start to come into play, are poorly understood.  In the end, your suggestion that matter is not “destroyed” when it enters a black hole but just becomes unobservable to us, is plausible.  Physicists cannot be definitive on this issue, though, as we just don’t have a good understanding of how gravity works at the center of a black hole.

Jeff Mangum

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How to Calculate Heliocentric Julian Date from a Given Julian Date and Object RA/Dec

Question: What is the algorithm for calculating Heliocentric Julian date from a given Julian date and object RA/Dec?  I would like this for a variable star application I’m writing.  — James

Answer: I would start with the online calculator provided by the British Astronomical Association.  If you are adventurous and you can program in Python, you might want to try the PyAstronomy routine for this calculation (which is, I believe, a port of the original IDL routine which does this calculation).  Finally, if you would like to do the calculations by-hand, check-out the Wikipedia page on Heliocentric Julian Date.

Jeff Mangum

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The Relative Timing Between Solar and Lunar Eclipses

Question: I’m working on a thesis for the chronology of the last month of Jesus life. According to NASA, as best I can make out, there was a partial Lunar Eclipse about sunset 6-7PM in Israel the day Jesus died, April 3, AD 33.  Also they record a total Solar Eclipse 2 weeks earlier about 1pm? March 19 AD 33 (I don’t think this event was observable from Israel).  My problem is if my understanding of NASA’S astronomical charts is correct there is a span of 15 and 1 quarter days between the 2 events but if half a Lunar Month (29.5 days) is 14 and 3 quarter days, how is it that there is a half a day difference?  I’m an unemployed carpenter not an informed astronomer. On my own I can’t work out the maths or fully comprehend the NASA charts.  Can you please confirm the exact time of the conjunction March 19 AD 33 in what would be Jerusalem time and how the intervening span is what it is, if it is not 14 and 3 quarter days?  — Glen

Answer: The NASA lunar eclipse information indicates that a partial lunar eclipse occurred on April 3, 33 CE with peak totality happening at about 16:47:51 local time in Jerusalem (14:47:51 UT).  NASA’s solar eclipse tables also indicate that there was a total solar eclipse on March 19, 33 CE with peak totality at about 12:50:14 local time in Jerusalem (10:50:14 UT), though it was not visible from Jerusalem.  The difference between these solar and lunar eclipses is about 15 days and 4 hours.  I believe that the reason why this time difference is not exactly one half of one synodic month (29.53 days) is due to the subtle differences between the lunar and solar orbits which dictate the periodicity of eclipses.  This periodicity, called the Saros cycle, has been known since ancient times and occurs due to the natural resonances between the synodic month, the time between orbital perigees, and time between orbital node crossings.  NASA’s “eclipses and the Saros” page contains all of the details regarding this recurrence for eclipses.

Jeff Mangum

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Tatoo Me with the VLA

Question: Hi.  Would you do me a favor to send to me through email the old aerial view graphic of VLA? It is like the Mercedes Benz logo without the circle, with a small rectangular at the intersection of the three arms.  I want to make a tatoo of that.  — Tao

Answer: We appreciate your dedication to the VLA!  We are not exactly sure which image you are looking for, so suggest that you look at what is available at  We hope that one of the images in our gallery is the one you are looking for.

Jeff Mangum

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